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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis
Mature bagworms


Posted by John Fulton -

Bagworms are an insect that conjures up images for many people. There are bagworms, and there are other larvae that live in a bag for at least part of their life cycle. We have bagworms, Eastern Tent Caterpillar, and Fall Webworms. For the true "bagworm," the insect that constructs a small bag like an ice cream cone from the leaf material of the tree or shrub it is on, the year-in and year-out treatment time for bagworms is June 15. You can mark this date on your calendar for next year and be within a few days of the correct treatment time. With a very cool spring, a week later may be a possibility This season's yo-yo temperatures really even out. The idea is to have all the eggs hatched before treatment.

The next problem is what to use. The traditional standby has been Sevin, but the B.t. products such as Dipel and Thuricide have really taken the majority of the market. Many other products will work, but the B.t. products have several good points including safety to mammals and toxicity to larger bagworms. Since they are bacteria that affect only the larvae of moths and butterflies, it does take a while for the bacteria to build up to the point where they can kill the bagworm. I won't get into the discussion about Monarch butterflies lighting in the tree just after treatment. And an item to note: there are several different strains of B.t. now on the market. One is for control of mosquito larvae, so make sure you get the correct one by reading on the label what insects will be controlled.

If you are in doubt about whether you have bagworms, check your trees and shrubs around June 15. You can actually see the small bags as the larvae build them. They become very noticeable at about 1/16 of an inch long. Treat bagworms early, since larger ones are more difficult to control, but try to ensure the eggs are all hatched out.

Most people think that bagworms only affect evergreens. Evergreens seem to be their preferred host group, but bagworms have a huge number of potential hosts. Through the years I have seen them on oak trees, grape vines, apples, and about any other growing thing you can think of.

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